Chemical recycling of post-consumer polymer waste over fluidizing cracking catalysts for producing chemicals and hydrocarbon fuels

Abstract

Mixture of polymer waste (LDPE/HDPE/PP) was pyrolyzed over various catalysts using a laboratory fluidized-bed reactor operating isothermally at ambient pressure. The systematic experiments discussed in this work show that the use of various catalysts improves the yield of hydrocarbon products and provides better selectivity in the product distributions. Typically, the yield of volatile hydrocarbons for zeolitic catalysts (ZSM-5 > MOR > USY) gave higher yield than non-zeolitic catalysts (MCM-41 > ASA). MCM-41 with large mesopores and ASA with weaker acid sites resulted in a highly olefinic product and gave a wide carbon number distribution, whereas USY yielded a saturate-rich product with a wide carbon number distribution and substantial coke levels. In addition, a model based on kinetic and mechanistic considerations associated with chemical reactions and catalyst deactivation for the catalytic degradation of commingled polymer waste has been developed. This model represents the benefits of product selectivity for the chemical composition in relation to the performance of the catalyst used and particle size selected as well as the effect of operation such as rate of fluidizing gas and reaction temperature. Moreover, it is demonstrated that conversion post-consumer LDPE/HDPE/PP polymer waste to volatile hydrocarbons was more than 80 wt% of feed in 20 min in the presence of cracking catalysts with fluidized-bed reactor used in this study. It is also shown that from a practical point of view, this study gives promising results as an alternative technique for the cracking and recycling of post-consumer polymer waste.